The present invention generally relates to rotary magnetic head devices, and more particularly to a rotary magnetic head device which is controlled of its height position so that rotary magnetic heads can accurately scan over tracks on a magnetic tape.
The assignee of the present application has previously proposed a system capable of recording and reproducing a color video signal on tracks which are formed on a tape without gaps between adjacent tracks, without being affected by beat disturbance. This previously proposed system is described in a U.S. Pat. No. 4,178,606 entitled "COLOR VIDEO SIGNAL RECORDING AND/OR REPRODUCING SYSTEM". According to this system, a pair of azimuth heads have gaps which are inclined by a certain azimuth angle in mutually opposite directions with respect to a direction perpendicular to the longitudinal direction of the track. Adjacent tracks are formed side by side in contiguous contact, without a gap or guard band formed therebetween. In order to prevent beat disturbance from being introduced in the color video signal, the phase of the chrominance signal is shifted by 90.degree. for every one horizontal scanning period. In addition, the direction of the above phase shift is reversed from one track to the adjacent track. According to this previously proposed system, the tape utilization efficiency is high because the tracks are in close contact with each other. Furthermore, beat disturbance is not introduced.
On the other hand, there was a conventional system wherein the video signal is recorded on a magnetic tape along parallel tracks which are formed obliquely with respect to the longitudinal direction of the magnetic tape. The tape may either be stopped or caused to travel at speeds different from the tape speed upon recording, in order to carry out a speedchange reproduction such as a quick-motion reproduction, slow-motion reproduction, and still-picture reproduction. However, because the tape speed upon reproduction is different from the tape speed upon recording during the speed-change reproduction according to this conventional system, the scanning locus of heads with respect to the tape upon reproduction becomes different from the scanning locus of the heads upon recording. As a result, a so-called tracking error is introduced.
When a tracking error is introduced during the speedchange reproduction in the previously proposed system described before, a so-called reverse tracking occurs partially. One of the heads scans a part of the track which is recorded by a head having the same azimuth angle as the other head, during the reverse tracking. With respect to the part of the track which is scanned under the reverse tracking, there is almost no reproduction of the recorded signal because of the azimuth loss. For this reason, when the tracking error is introduced, the level of the reproduced signal drops, and noise accordingly appears at irregular positions on the reproduced picture. Therefore, the noise part in the reproduced picture moves, and the signal-to-noise level of the entire reproduced picture becomes poor, and it is impossible to obtain a speed-change reproduction picture of high quality.
Accordingly, as a system for compensating for the tracking error upon changed-speed reproduction, there was a conventional system wherein a swinging device using a bimorph which comprises a pair of piezoelectric elements is separately provided for each of a pair of rotary magnetic heads of a rotary body. In this system, the magnetic heads are independently swung by the respective swinging devices, and control is carried out so that the magnetic heads accurately scan over the correct tracks.
However, this conventional system had disadvantages in that: (a) the construction of the apparatus becomes complex because there is a need to provide a swinging device for each of the rotary magnetic heads; (b) the tracking control cannot be carried out satisfactorily with respect to the magnetic heads in a mutually interrelated manner when there is inconsistency between the operations of the swinging devices; (c) the hysteresis of the operation becomes large; (d) a brush is required because a control voltage is applied to the swinging devices provided in the rotary body; and (e) a large swinging quantity cannot be obtained.
In addition, the conventional swinging device is designed so that the magnetic head is provided at the tip end of the bimorph and the rear end of the bimorph is fixed, to swing the magnetic head provided at the tip end of the bimorph upwards and downwards according to the bend in the bimorph. Hence, because the magnetic head is swung upwards and downwards by the swing at the tip end of the bimorph which swings about the fixed rear end, the magnetic head is in a horizontal state in its neutral position but is inclined upwards and downwards at the positions swung upwards and downwards, respectively. For this reason, the magnetic head does not make perpendicular contact with the magnetic tape at positions other than its neutral position. That is, the head gap does not entirely make contact with the magnetic tape at the positions other than the neutral position of the magnetic head, and results in an output loss at such positions other than the neutral position of the magnetic head. Thus, in this conventional system, even if the tracking control is carried out correctly, there were big disadvantages in that the output signal level decreased and the quality of the reproduced picture becomes poor. Particularly when diameter of the guide drum is set to a small value, the inclination of the magnetic heads becomes large, and the above disadvantages becomes even more notable. Therefore, it becomes difficult to reduce the diameter of the guide drum and reduce the overall size of the recording and reproducing apparatus.
Moreover, in order to overcome the aforementioned disadvantages (a) through (e) of the swinging device using bimorph described hereinbefore, a magnetic head swinging device was proposed in a U.S. patent application Ser. No. 178,852 (U.S. Pat. No. 4,365,279) in which the assignee is the same as that of the present application. In this proposed apparatus, a rotary body provided with a pair of magnetic heads along its diametral direction is supported at the center thereof to freely swing so as to undergo a so-called see-saw operation. According to this proposed apparatus, the construction of the apparatus becomes simple compared to the conventional apparatus which requires a swinging device for each of the magnetic heads, because the pair of magnetic heads in this proposed apparatus constantly undergo swinging in relation to each other. Further, there is an advantage in that problems such as the inconsistent operations between the swinging devices, are not introduced. However, the magnetic heads are also swung upwards and downwards about the center of rotation of the rotary body in this proposed apparatus. Hence, in states where the magnetic heads are swung upwards or downwards, the magnetic heads are inclined upwards or downwards. For this reason, the latter serious disadvantages of the previously described conventional apparatus, that is, the disadvantages in that the magnetic heads do not make perpendicular contact with the magnetic tape and the head gaps do not entirely make contact with the magnetic tape to introduce the output loss, are not eliminated in this proposed apparatus. In addition, although the gap between a rotary yoke and a coil must be set to a minimum in order to increase the driving force, the rotary yoke swings, and the above gap must be set large to a certain extent so as not to interfere with the swinging of the rotary yoke. As a result, a large driving force cannot be obtained, and there was a disadvantage in that degradation is introduced in the scanning characteristics of the magnetic heads.